1. Field of the invention
The present invention relates to an organic EL device, and a method for forming it.
2. Description of the Related Art
An organic EL (Electroluminescence) device is a luminescence device having a stacked structure in which a lower electrode is formed above a substrate, an organic material layer including a luminescent layer is formed in a single- or multi-layer form above the lower electrode, and an upper electrode is formed on the organic material layer, whereby the organic material layer is interposed between the pair of electrodes. One of the upper and lower electrodes is used as an anode, and the other electrode as a cathode. When a voltage is applied between the electrodes, electrons which are injected and transported from the cathode into the organic material layer recombine with holes which are injected and transported from the anode, thereby causing luminescence. Recently, such an organic EL device receives attention as a thin luminescence device which can provide surface luminescence, and which constitutes a light source for various purposes or a display unit of a self-luminous thin display device.
In such an organic EL device, it is known that, when the stacked member (organic EL device layer) configured by the organic material layer and the electrodes is exposed to the outside air, luminescence characteristics are impaired. In order to enhance the stability and durability of luminescence, therefore, a sealing for blocking the organic EL device layer from the outside air is indispensable. Usually, such sealing means is realized by bonding a passivation film onto a substrate on which an organic EL device layer is formed, so as to cover the layer, and placing the organic EL device layer in a sealing space which is formed between the substrate and the passivation film.
By contrast, in order to cope with the increased kinds of display panel forms due to further thinning, employment of a flexible substrate, and the like, various sealing techniques have been proposed (see Patent References JP-A-10-312883, JP-A-11-97169).
JP-A-10-312883 discloses a technique in which a passivation film covering an organic EL device layer is configured by two layers of a buffer film covering a defect portion, and a barrier film formed by a thin film which is stacked on the film. JP-A-11-97169 discloses a technique in which a glass modifying material composed of an element such as Sc or Ce, or an oxide or sulfide of such an element is doped into a glass forming material (host) composed of an oxide or sulfide of an element such as Si or Zn, and the resulting material is subjected to sputtering at a low temperature, or a vapor deposition method such as ion beam or ion plating, thereby forming a protective layer covering an organic EL device layer.
In these conventional techniques, the barrier film or the protective layer is grown by sputtering or vapor deposition. Therefore, such a film or layer can be usually grown only at a rate as low as about several nm/sec. Consequently, the film growth process requires a long time period, and a film having a sufficient gas barrier property cannot be formed in view of the reduction of the required time period. In the conventional techniques, moreover, a large residual stress is applied to the barrier film, and hence cracks easily occurs, with the result that the thickness of the film cannot be largely increased. As a countermeasure against this disadvantage, the buffer film is interposed to relax the stress. In the configuration where only the buffer film is used, however, film growth which is sufficient for relaxing a residual stress cannot be conducted.
In the conventional art, a film is grown by a method in which a film material is caused to scatter in a film growth chamber. Therefore, such a film growth method has disadvantages that the utilization efficiency of the material is poor. To ensure a larger thickness is in the film growth, the material is used more wastefully.